Braking circuits of known type comprise a master cylinder boosted by a pneumatic brake booster, the braking circuit being actuated by a control rod connected to a brake pedal. Brake circuits also increasingly often comprise brake regulating devices so as to prevent the wheels from locking under emergency braking and thus improve the driver's control of the vehicle, these devices are known as ABS devices. ABS devices comprise an electronic computer gathering information from sensors arranged at the wheels of the vehicle so as to detect the locking of the wheels; ABS devices also comprise electrically operated valves, at least one pressure accumulator, a hydraulic pump, for example an electric pump for supplying pressurized brake fluid.
When the computer of the ABS device detects that wheels are becoming locked, the computer initially releases the braking at the wheels close to locking and then increases the pressure of the brake fluid at these wheels in order to brake them once again, and to do, that, the hydraulic pump is brought into operation. The operation of the ABS device is likely to cause vibration, this vibration being transmitted to the entirety of the hydraulic circuit and causing noise to occur. This noise is annoying to the driver, on the one hand for his driving comfort and, on the other hand, because he may worry that his braking circuit is not operating correctly.
The Applicant Company has discovered that this vibration is transmitted via the master cylinder to the booster, then via the booster to the bulkhead separating the engine compartment from the cabin of the vehicle and also to the pedalbox. This vibration is therefore a source of noise, the booster being particularly sensitive to this vibration because of the small thickness of the sheet metal of which the outer wall of the booster is made. In addition, vibration at the pedalbox gives the driver of the vehicle an unpleasant feeling.
Devices are known that reduce the noise caused by vibration in the wheel cylinders when the ABS device is in operation, these comprising a sensor associated with each wheel cylinder and transmitting to the electronic control unit a signal corresponding to the noise caused by the vibration. The control unit then sends a signal to the electrically operated valves so as to regulate the pressure of the brake fluid supplied to each wheel cylinder and cause vibration at a predetermined frequency so as to cancel the vibrations due to the operation of the ABS device. However, this device is very expensive, difficult to implement, and requires very minute adjustments.